Pressure casting machine injection pressure control



Dec. 19, 1944. LESTER ET AL 2,365,282

PRESSURE CASTING MACHINE INJECTION PRESSURE CONTROL Filed June 15, 19402 Sheets-Sheet l INVENTOR5 NATHAN LESTER Clnd WILLIAM H.SCHWARTZ.

ATTORNEYS Dec. 19, 1944. N. LESTER ET AL PRESSURE CASTING MACHINEINJECTION PRESSURE CONTROL Filed June 15, 1940 2 Sheets-Sheet 2INVENTORS N ATHAN LESTER and 1Z3: WEDOWUNF- UZDJO 13-:

BY WILLIAM HSQHWARTZ. MIOEMM1, a./

ATTORNEYS Patented Dec. 19, 1944 PRESSUR CASTING MACHINE INJECTIONPRESSURE CONTROL Nathan Lester, Shaker Heights, and William H. Schwartz,Cleveland, Ohio, assignors to Lester Engineering Company, Cleveland,Ohio, a corporation of Ohio Application June 15, 1940, Serial No.340,834

4 Claims.

This invention relates to a process, and apparatus adapted to conformwith that process, for controlling the application of motivatingpressure to the injection cylinder of a pressure casting machine. It hasbeen well-recognized by those skilled in the art of designing, buildingand operating pressure casting machines, that a difficult problem existswith respect to the satisfactory transfer of the material to be castfrom the casting chamber to the mold cavity. Such material, whether itbe of a non-metallic nature such as a plastic, or a metallic materialsuch as white metal, and in the case of a pressure casting machineoperating upon the injection principle, must first be transformed into astate of proper and desired fluidity before it is injected into themold. This transformation is usually accomplished by the application ofheat to a pressure cylinder or chamber in which the material to be castis first deposited. The material is then injected from this pressurechamber through a connecting conduit, usually termed the injectionnozzle, into the mold cavity, where it subsequently becomes solidifiedand is thence removed to produce the resultant casting. During suchtransmission of the material from the pressure cylinder or chamber tothe mold cavity, it, of course, undergoes various changes in itsphysical properties, and this phenomenon, together with the circumstancethat the material is filling a confined space, viz., the mold cavity,results in a variation in the resistance to the injection pressure ormotivating force applied to the material during the casting stroke. Andthis resistance to'injection pressure, of course, undergoes sudden andrapid increase near the end of the injection stroke as the mold cavityis filled with material.

Thus, it is important that a steady, positive and controlled injectionpressure be applied during the major portion of theinjection castingstroke, and that an increased pressure be applied and maintained nearthe end of such stroke and responsive to the sudden increase inresistance or sudden pressure build-up in the injection cylinder.

The problem which has been presented, and now solved by our instantinvention, therefore, consists in so controlling and regulating thepressure applied to the injection cylinder of-a pressure castingmachine, as to obtain the proper coordination between the force appliedand the variable resistance to that force.

Our invention is productive of the further advantage in that there is asubstantial increase in economy of operation. due to the elimination ofpower loss and decrease in the amount of time required per workingstroke of the machine. Furthermore, our invention has produced the nu:-expected and unusual result in that the castings produced by the machineoperating according to the principle, of our invention, have asubstantially increased density, stronger physical structure, and moresharply and closely defined conformity to casting specification limits,than has heretofore been achieved upon similar pressure casting machinesnot operating under our injection pressure control process. Theseadvantages and novel results will be explained in fur-- ther detail asthe following description proceeds:

To the accomplishment of the foregoing and related ends, said invention,then, consists of the means heremafter'fully described and particularlypointed out in the claims. The annexed drawings and the followingdescription sets forth in detail certain means and one mode of carryingout the invention, such disclosed means and mode illustrating, however,but one of various ways in which the principle of the invention may beused.

In said annexed drawings- Fig. 1 is a side elevational view, partiallyin section, of a representative pressure casting machine to which theoperating process and control apparatus of our invention may be applied;and

ings, and Fig. 1 thereof, there is shown therein a pressure castingmachine of the injection type, which, in this particular instance, isadapted to cast a metallic material, such as white metal. This machineconsists of a base I, a melting pot,2 mounted in the furnace 3, and witha pressure cylinder or chamber 4 in which a piston 4 is adapted to bereciprocated through connection with the hydraulic cylinder 5. A passageor gooseneck 6 leads from the cylinder 4 to the nozzle 1 and thence, tothe mold cavity 8 defined by the separable die blocks 9 and Ill. The dieblock I0 is mounted upon the stationary die plate I l and the die block9 is carried by the movable die plate l2. A hydraulic die-movingcylinder l3 connects through the medium of the connecting rod l4 andtoggle link mechanism l5 to the movable die plate [2, to move the lattertoward dicated at It. An electric drive motor connects through the shaftII to the hydraulic pressure pumps, which are not shown in Fig. 1, sincethey are contained within the base of the mainterior of thebase Controllevers are mounted With theessential elements oi the pressure castingmachine, as above described, now in mind, attention is directed to Fig.2, which is a diagrammatic representation of the pertinent operatingelements and fluid pressure control solenoid-actuated valve 33, fromwhich the lines 51, 53 communicate-lwith the distributing valve 55. Themovable valve element or spool 64 in the valve 53 is' normally held in aleithand posichine; A removable panel l3 gives access to the 5 tion,placing'the feed line in communication with the line 51, .by means ofthe compression spring 55. The spool 54 is moved in a righthanddirection by means of the electric solenoid 6G, to

o 58. A drainline 51 connects the valve 53 to the lines and connectionscomprising the control sysboth the high volume, low pressure pump 30 andthe low volume, high pressure pump 3|. Thus, at

the same speed of rotation, the pump 30 will be most efllciently adapted,to deliver, for example, fifty gallons per minute of fluid at 300pounds pressure; whereas, the pump 3| will be adapted to deliver onlyseven gallons per minute at 1000 pounds pressure.

The intake lines 32 and 33 of the pumps 30 and 3|, respectively, jointhe common intake line 34 which, in turn, leads from the reservoir 35-.The discharge-line 35 from the pump 30 leads to the one end of the main,through passage 31 of the by-pass valve 33. The plunger 39 seats in theupper end of the by-pass passage 40 of the valve 38 and normally holdssuch passage 40 closed to the drain line 4|. The drain line 4| connectsto the main drain line 42, returning to the reservoir 35.

The line 43 leads from the outlet end of the through passage 31 of theby-pass valve, through the check valve 44, to the main pressure deliveryline 45'. The line 45 connects to the pump'3l, and a relief valve 45 isconnected in it in order to serve as a safety valve to limit the maximumpressure obtainable in the line 45. The relief valve '45 is, of course,connected by the drain 4'! to themain drain line 42.

The main delivery line 45, directing attention to the righthand portionof Fig. 2, is connected directly to each one of the operating ordistributing valves for the die cylinder, the ejection cyl- -inder andthe injection cylinder. Thus, the line connects to the solenoid-actuateddistributing valve 43 which has one line 49 leading to one end of thedie cylinder |3 and another distributing line 50 leading to the otherend of the die cylinder I3. The line 45 also connects directly to asimilar solenoid-actuating distributing valve 5|, connected through thedistributing lines 52 and 53 to alternate ends of the ejection cylinderIS.

A drain line 54 connects the distributing valves. 48 and 5| to the maindrain line 42. Likewise the line 45 connects directly to thepressure-actuated distributing valve 55. This distributing valve is ofthe dumb-bell" or spool type comprising the spool. 55 adapted toslidewithin the main cylindrical chamber of the valve. Shifting 0rsliding of the spool 55 is accomplished by means of pressure introducedat opposite ends of the valv 55 through the lines 51 and 53 to the endchambers 55 and 50, respectively, of the valve housing. Distributinglines 6|, 52 lead from the distributing valve 55 to opposite ends of theinjection cylinder 5. A drain line 54' connects the valve 55 to thedrain line 54, then to the main drain line 42.

Th main pressure line 45 also connects to the main drain line 42. I

The line 83 connects to the line 3| leading to the head end of theinjection cylinder 5. A line 53,, in turn, connects the line 33 tothe-pressureactuated spool valve 10 in which the spool 1| is normallyheld in such a position by means of the compression spring l2 as to openthe end of the line 53. The spool II is moved by means of pressure inthe chamber -13 in the end of the valve to close the line 63 to theconnecting line 14, to

the intake passage 15 of the flow control valve 15. The flow controlvalve 16 has a poppet type valve 11, normally urged to open position bythe compression spring 11'; and also a throttle valve 18 locatedadjacent the outlet to the drain line 19 connecting to the main drainline. 42. The passage 80 leads to the under-sidev of the piston 8| onthe stem of the p ppet valve 11, to close the latter against thepressure of the spring Tl when flow through the control valve I5 reachesits maximum predetermined capacity.

The pilot line 92' leads from the chamber 13 of the valve 10 to anoutlet line.32 which leads from the solenoid-actuated valve 81 to theunder side of the piston of the plunger 33. The compression spring 35,adjustable as to compression by means of the threaded screwB6,-'n0rm'ally urges the enlarged head or piston of the plunger 39against its seat in the outlet passage 40.

The valve 81 is similar to the valve 53, having a spool 83 normallyurged in a righthand direction by means of the compression spring 89 andmoved in a lefthand direction by means of the solenoid 00. The line 9|connects the main de- 5 livery line 45 from a point immediately adjacentthe pump 3|, to the inlet of the valve 31. A distributing line 82connects the other outlet of the valve 81 to the upper-side of thepiston on the plunger 39 in the chamber 84. The drain line 94 50connects the valve 81 to the main drain line 42.

The pilot line 53 terminates in the chamber 39 r of thepressure-actuated electric switch 95, which is normally held in closedposition by the compression spring 95. Thus, as the piston 91 carries 55the switch bar 98 in a righthand direction and 5 panel 20.

against the pressure of the compression spring 95 (adjustable as topressure by the screw 95'), electric contact is broken through the wiresI00 and IN leading to the solenoid to deenergize the latter. The circuitof the wires I00 and IM derives power from the wires I02 and W3 leadingto a suitable electric power source. The switch I04, connected in thiscircuit is operated by being connected to the manual control lever A onthe operation, is in the position as shown in Fig, 2, whereby. pressureis led through the main. delivery line 45 to the line 51 to move thespool 56 of the valve 56 in a lefthand direction into the position"opposite to that shown in Fig. 2, so that pressure from both ofthepumps 30 and 3| is delivered to the line 62 to the rod end of theinjection cylinder, whereupon the casting plunger 4' is held at theupper end, or initiating point of its casting stroke. Up to this point,it will be seen that pressure from the high volume, low pressure pump'30, passes from the line 36 through the by-pass'valve 38 to the line 43and joins with the fluid delivered from the pump 3|. in the line 45.During this time, viz., preparatory to the working stroke of theinjection cylinder 5, or before the machine is ready to deliver itsinjection shot," all of the various hydraulic cylinders 5, I3 and I6 aremoved with comparative ease and rapidity. Hence, the pump 30 is bestsuited to deliver the major portion of the hydraulic pressure required.As these hydraulic cylinders 5, l3 and I6 reach the end of theirpreparatory stroke positions, it is no longer feasible or efficient tomaintain a holding pressure in them by means of the pump 30, but on thecontrary, this pump should be disconnected from the main pressure line45 and such holding pressure maintained by the low volume, high pressure pump 3| which is most suitably and efficiently designed to do so.This maintenance of connection of both of the pumps 30 and 3| to jointdelivery to the main pressure supply line 45 is achieved as follows:

Pressure from the line 9| enters the valve 81 and since the latter is inthe position as shown in Fig. 2. such pressure is delivered to the line92. to the under-side of the by-pass valve plunger 39, tending to raisethe latter and-to allow pressure from the line 36 to pass o-utthroughthe bypass outlet 40. Thus, for example, if the by-pass valvecompression spring 85 is set at a point corresponding to a pressure of300 pounds per square inch, as soon as this pressure is attained inlines 9| and 92, the valve plunger 39 will be raised against the springpressure and the pump 30 thus disconnected at the point where it hasachieved its maximum operating pressure efliciency, leaving the pump 3|to supply any needed additional pressure such as, for example, inholding the die cylinder 3 and the ejection cylinder l6 in closedposition, or in holding the piston in the injection cylinder 5 at theupper end of its stroke. At this point in the operation of the castingmachine and the control system, the injection cylinder 5 is ready tostart upon its injection shot or working stroke, which is initiated bymanipulation of the lever A on the control panel 20, which iselectrically connected to the solenoid 66 and also connected to theswitch I04. The solenoid 66 on being energized, moves the spool 64 in arighthand direction to connect the main line 45 to the line 58 to movethe spool 56 in a righthand direction and in the position as shown inFig. 2, whereby pressure from both of the pumps 30 and 3| is deliveredto the line 6| t0 the head end of the injection cylinder to start theplunger 4' on its injection stroke. At the same time, the switch I04being closed, and the switch 98 closed by the pressure of the spring 95,the circuit in the wires I00 and |0| is closed to energize the solenoid90, to move the spool 88 in a lefthand direction. This places the line9| in communication with the line 82, whereby pressure is directed tothe upper side of the by-pass valve plunger 39 to hold it in a downwarddirection, preventing the outlet passage 40 from opening, even thoughthe delivery pressure of the high volume, low pressure pump 30 mightexceed its optimum capacity of 300 pounds per square inch. 1

Thus, during the initiation and major portion of the injection orworking stroke of the cylinder 5, both pumps 30 and 3| areworkingtogether as a team to give a positive, constant motivating force on theinjection stroke. If any minor resistance is incurred during thisstroke, the pump 30 will not be disconnected, but rather will its workbe augmented by the higher pressure capacity of the pump 3|, so thatthere is no hesitance in the injection or "shot. stroke of the plunger4'. Thus, for example, if the pressure requirement in the injectioncylinder 5 during its working stroke should vary from 200 to 500 poundsper square inch as an incident to theresistance of movement to the;material being cast, the pump willnot be intermittently connected anddisconnected to the main delivery line 45 which would otherwise producea variation in the rate of travel of the casting; plunger 4', but willremain connected so that both pumps so deliver their'pressure as tomove; ifthe plunger 4' surely and uniformly throughout the major portionof its stroke.

During this injection stroke, pressure built up in the line 6| istransmitted through the line 68' to two respective pumps.

the valve 96, which is set at such a predetermined point that the piston91 will be moved to open the switch -98, thus de-ene'rgizing thesolenoid 90, moving the spool 88 in a righthand direction and placingthe line 9| in communication with the line 92, to raise the plunger 39and allow fluid to flow out through the outlet 40 of the by-pass valve38. It has previously been indicated by way of example, that a suitabledelivery pressure for the pump 30 might be 300 pounds per square inchand for the pump 3|, 1000 pounds per square inch, as the most efficientoperating pressures for these Thus, the valve 96, in such an exemplarysituation, should be set at 1000 pounds per square inch, whereupon, thepump 30 would be shunted or by-passed to discharge when its high volumecapacity is no longer needed.

The check valve 44, of course, prevents the increased pressure in theline 45 from passing back through the line 43 to the by-pass Valve 38.By effecting this automatic disconnection of the pump 30, the power lossincident to operating it under pressure and volume conditions derogatoryto efficiency, is substantially reduced.

The flow control feature of our system as embodied principally in thefunction of the valves 10 and 16, is also interdependent with thelastdescribed automatic disconnection feature of the high volume, lowpressure pump. This flow control feature of our system operates asfollows:

As the piston in the cylinder 5 begins its stroke upon introduction ofpressure through the line 6|, pressure on spool 13 of valve 10 frompressure line 92' is released due to solenoid of valve 81 energizing andshifting its spool, opening pressure in line 9| to line 82 and line 92to drain 94. The valve 10 then opens to the line 69, to the line 14, tothe flow control valve 16. This latter valve so functions as to limitthe maximum rate of flow from the main delivery line 45 to the line 6|and it does so, not by throttling or metering the fluid flow in the line6|, but by bleeding off' or withdrawing the excess above apredetermined:

maximum. The reason for so controlling .the'

cylinder at an optimum rate. This rate, of course, can be controlled bythe rate of introduction of fluid through the line I. The obviouscontrol of the maximum rate of flow in the linev BI is no longernecessary so the flow control valve 16 is rendered inoperative.

This is accomplished by the connection of the line 92 to the pressureline 9|, through the shifting or the valve 81. At the same time, spoolII is forced against spring 12 which closes oil the end of the line 69.This prevents the pump 3| delivering its small volume through the flowcontrol valve It, thus eliminating a drop of pressure throughout thesystem.

It will thus be seen that through the operation of our flow controlsystem, that the plunger 4' is caused to move at a uniform, controlledand ellicient rate during the major portion of its injection stroke,with an automatic response of the pressure system to the suddenincreased resistance to the travel of such plunger near the end of itsstroke.

The above-described control system andmethod of operation thereof hasresulted in a new 1 method of injection casting, which also forms a partof our present invention. Heretofore, in injection casting, it has beenfound necessary to so maintain the temperature in the passage leadingfrom the casting cylinder to the mold cavity as to prevent a freezingout or loss of fluidity of the material passing therethrough. Thus, for'example, means have been provided to heat the nozzle 1. On the contrary,and by means of our present invention, we purposefully permit thetemperature in the nozzle 1 to drop below melting .or permit thetemperature in the nozzle I to drop below melting or fluidity point ofthe material to be cast so that a small gate slug is formed in its endcommunicating with the gate to the die cavity 8. The formation of thisgate slug prevents the material to be cast from prematurely passing intothe mold cavity 8 and not until the nozzle 1 and gooseneck 6 have beencompletely filled with material and air otherwise entrapped therein hasbeen evacuated. Such accuses cylinder to the mold cavity, which couldnot be overcome regardless of the pressure applied to the material andwithout'the application of external heat to such passage to again renderfluid the material therein.

We have unexpectedly discovered that cas ings made according to ourlast-described novel casting method and with a machine towhich ourabove-described flow control system has been applied, possess muchgreater density, improved grain structure, and closer conformity tocasting specifications than have otherwise been obtainentrapment of air,of course, has heretofore been carried over with the material to be castinto the mold cavity 8, resulting in a porosity in the resultantcasting.

The sure and positive application of hydraulic pressure to move ourcasting plunger 4' during this injection stroke renders it possible topermit this gate slug to form in the end of the nozzle I withoutinvolving heretofore objectionable conditions, such asa sudden pressuredrop in the injection cylinder nozzle after the resistance necessary todislodge the gate slug has been overcome. Such a sudden pressure dropwould possibly prove fatal to the entire casting operation in that itwould permit the melting point of the material under pressure to lowerand hence, to freeze out or solidify throughout the entire length of thenozzle I, to thereby resultin a clogging of the passage from the castingable. Thus, for example, in the case of the making of white metalcastings, those produced from a machine controlled according to ourpresent invention, have averaged about 7% greater density than could beproduced heretofore on the same machine, not operated with our controlsystem.

Other modes of applying the principle of our invention may be employedinstead of the one explained, change being made as regards the means andthe steps herein disclosed, provided those stated by any of thefollowing claims or their equivalent be employed.

We, therefore, particularly point out and distinctly claim as ourinvention:

1. Injection pressure control mechanism for a pressure casting machinecomprising an injection cylinder, a plurality of fluid pressure supplypumps, each having different volume and pressure delivery capacities,conduit means, jointly connecting all of said pumps to said cylinder,pressure responsive means connected to said conduit means and actuatedby a pressure variation therein for disconnecting one of said pumps fromsaid conduit means, flow control valve means con-' nected to saidconduit means for regulating the rate of fluid flow therein, and meansfor rendering said flow control valve. means inoperative duringdisconnection of said one of said pumps.

2. Injection pressure control mechanism for a pressure casting machinecomprising an injection cylinder, a plurality of fluid pressure supplypumps, each having diflerent volume and pressure delivery capacities,conduit means, jointly connecting all of said pumps to said cylinder,valve means connecting those of said pumps having relatively highervolume capacity to free discharge, flow control valve means connected tosaid conduit means for regulating the rate of fluid flow'therein andpressure responsive control means connected to said conduit means, tosaid first valve means and to said flow control valve means, saidpressure responsive controlmeans being adapted to open simultaneouslysaid first valve means to free discharge and to render said flow controlvalve means in-' operative on increase of pressure beyond apredetermineddimit in said conduit means.

3. Injection pressure control mechanism for a pressure casting machinecomprising an injection cylinder, a high volume, low'pressure capacitypump, a low volume, high pressure capacity pump, a conduit connectingboth of said pumps to said cylinder, a flow control valve adapted toregulate fluid flow in said conduit by bleeding oil a portion of thefluid passing therethrough, a bypass valve adapted to connected saidfirst-named pump to free discharge, and control means actuated by apredetermined pressure in said conduit for opening said by-pass valveand rendering said flow control valve inoperative.

4. Injection pressure control mechanism for a pressure casting machinecomprising an injecliqueiy or tion cylinder, a high volume, low pressurecapacity pump, a low volume, high pressure capacity pump, a conduitconnecting both of said pumps to said cylinder, a by-pass valve adaptedto connect said first-named pump to free discharge, said by-pass valvebeing pressure-actuated, a second conduit leading from said second-namedpump, a flow control valve adapted to regulate the rate of fluid flow insaid first conduit by bleeding ofi a portion of the fluid passingtherethrough, said flow control valve being pressure-

